WE CLAIM:
Claim 1. A clamp device (10) configured to clamp a workpiece by a rotatable clamp arm (18), comprising:
a clamp body (14):
a driving unit (12) provided on the clamp body (14):
a rotating shaft (90) configured to rotate together with the clamp arm (18) in an integrated manner under operation of the driving unit (12):
a detection target (20, 150, 170, 180, 190, 200) made of metal and provided on the rotating shaft (90) so as to extend around an axis of the rotating shaft (90): and
one proximity sensor (22) disposed so as to face the detection target (20, 150, 170, 180, 190, 200) and configured to generate an eddy current in the detection target (20, 150, 170, 180, 190, 200) and detect magnetic loss;
wherein the detection target (20, 150, 170, 180, 190, 200) has a plate shape, and includes a long groove (112, 154, 156, 184, 186) extending in a direction along which the detection target (20, 150, 170, 180, 190, 200) extends, so that an area of a sensor facing part (126) of the detection target (20, 150, 170, 180, 190, 200) that faces a detector surface (124) of the proximity sensor (22) changes with rotation of the rotating shaft (90).

Claim 2. The clamp device {10) according to claim 1, wherein a side {112a, 112b, 154a, 156a) of the long groove {112, 154, 156) linearly extends in a direction intersecting with the direction along which the detection target {20, 150, 170, 180, 190, 200) extends.
Claim 3. The clamp device {10) according to claim 1, wherein a side {184a, 186a) of the long groove {184, 186) extends in a curved manner.
Claim 4. The clamp device {10) according to any one of claims 1, 2, and 3, wherein:
the long groove of the detection target {20) includes one long groove {112); and
the sensor facing part {126) extends over both sides of the long groove {112).
Claim 5. The clamp device (10) according to any one of claims 1 and 2 to 4, wherein:
the long groove of the detection target (150, 170, 180, 190, 200) includes two long grooves (154, 156, 184, 186) arranged side by side in a width direction of the detection target (150, 170, 180, 190, 200); and
the sensor facing part {126) is disposed between the two long grooves (154, 156, 184, 186).
Claim 6. The clamp device {10) according to claim 5, wherein:

the detection target (170, 190, 200) includes a communication groove (174, 194) through which ends of the two long grooves (156 184, 186) communicate with each other: and
a groove width of the communication groove (174, 194) is greater than or equal to a diameter of the detector surface (124).
Claim 7. The clamp device (10) according to any one of claims 1 and 2 to 6, wherein the detection target (20, 150, 170, 180, 190, 200) is secured to the rotating shaft (90) by a screw member (114).
Claim 8. The clamp device (10) according to claim 7, wherein an attachment portion (110) having an insertion hole (116) into which the screw member (114) is inserted is disposed at at least one end of the detection target (20, 150, 170, 180, 190, 200) in the direction along which the detection target (20, 150, 170, 180, 190, 200) extends.
Claim 9. The clamp device (10) according to claim 7 or 8, wherein holding portions (202, 204) configured to hold an outer circumferential surface of the rotating shaft (90) from outside in radial directions are disposed at both ends of the detection target (200) in the direction along which the detection target (200) extends.
Claim 10. The clamp device (10) according to any one of claims 1 and 2 to 9, wherein a recess portion (106) is formed in a region of an outer circumferential

surface of the rotating shaft (90) that faces the detector surface (124) .